1. Field of the Invention
This invention concerns an integrated circuit device and, more specifically, it relates to an integrated circuit device in which a plurality of electrodes are disposed by at least two layers by way of an inter-layer insulation layer on an insulation substrate.
This invention also relates to a heat-sensitive recording thermal head and a method of manufacturing the same.
2. Description of the Prior Art
An integrated circuit in which a plurality of electrodes are disposed on an insulation substrate by at least two layers by way of an inter-layer insulation layer has widely been utilized, for example, as a thermal head for use in heat-sensitive recording. If there are pin holes in the inter-layer insulation layer between the two layer electrodes in the integrated circuit device, electroconduction is caused by the pin holes.
In conventional heads having heat generating elements localized to the end of an insulation substrate such that electrical supply leads are led out only from one side of the array of the heat generating elements in order that the structure is simplified by using only a set of circuit boards, printing images are observed just after the printing and no printing dusts are accumulated at the surface of the insulation substrate, it has been known so far to minimize the conductor width of the lower layer electrode so as to decrease the area where the upper layer and the lower layer electrodes intersect each other for preventing the pin hole-induced electroconduction as described above (Japanese Patent Laid-Open No. 95484/1982). If the area of the lower layer electrode is thus reduced, it results in problems that a uniform formation of the inter-layer insulation layer by utilizing the plasma reaction is difficult since the substrate is made of insulating material, that the thick portion of the film is peeled off or cracked or that pin holes are liable to be formed in the thin film portion.
Further, the thermal head for use in heat-sensitive recording is constituted such that the heat generating portion is selectively heated in a dot-like manner by recording electric signals in a state where it is abutted against paper to be recorded such as heat sensitive paper directly or by way of an ink film and recording is performed to the recording paper by the selective heating. The electrical signals are applied from the integrated circuit (hereinafter simply referred to as IC) portion to individual opposing electrodes.
Generally, the head for use in heat-sensitive recording is so constituted that a glaze layer is disposed on the heat insulation substrate, for flattening the surface and controlling the heat dissipation, the heat generating layer is deposited thereover, and a common electrode and individual electrodes (signal electrodes) opposing to each other with a gap are deposited on the heat generating layer. Then, the electrical signals are sent from the IC to the individual electrodes, by which the heat generating portions (gap portions) are selectively heated in a dot-like manner, and recording is performed on the recording paper such as heat-sensitive paper disposed at the upper surface thereof. In this case, since the resistor body situates to the inner side from the end of the head by the width of the common electrode, printed matters can not be read directly after the printing to provide a problem for increasing the printing speed. In view of the above, it has been attempted to situate the resistor body at the end of the head by employing a multi-layered wiring structure in which the common electrode is disposed below the resistor body.
In this case, if there are a number of heat generating portions selectively heated, the heat calorie transmitted to the lower part of the heat generating portions is increased and the temperature just below the resistor body is also increased and, accordingly, an insulation layer capable of withstanding high temperature is required. Further, if the part below the resistor body is heated to a high temperature, the alkali ingredient in the glaze layer (usually composed of SiO.sub.2 glass powder) diffuses to intrude into the heat generating layer to change the resistance value of the heat generating layer making it instable, as well as reducing the working life. An insulation film is interposed for preventing this and for insulation between the lower and upper layer electrodes.
Known inter-layer insulation films used so far include (1) thick film glass (for instance, as disclosed in Japanese Patent Laid-Open Nos. 53-87238 and 59-91072), (2) polyimide film (Japanese Patent Laid-Open Nos. 59-54578 and 59-79776) and (3) SiO.sub.2 evaporation deposition film by vapor deposition or sputtering (Japanese Patent Laid-Open Nos. 53-87238 and 53-87239).
However, since the sintering temperature for the glass film (1) is as high as 800.degree. C., it is also required for the lower layer electrode that is made of a thick film of a noble metal series such as of Pt or Pd.
Although the sintering temperature for the polyimide film (2) is as low as 300.degree.-400.degree. C., the production step is complicated in view of the thick film printing and, particularly, there is a problem that it is not resistive to high temperature.
The SiO.sub.2 evaporation deposition film by the vapor deposition (3) often causes pin holes due to the low density and, particularly, electroconduction is liable to be caused between the upper and lower layer electrodes in the place where there are remarkable unevennesses such as ceramics. Further, in the vapor deposition of SiO.sub.2 by sputtering, since the SiO.sub.2 growing speed is as low as from 50 to 100 .ANG./min, the coating velocity is low and it does not suitable to the mass production.